Voltammetric cells, using electrochemical techniques for analysis, generally comprise a vessel receiving the solution to be evaluated, a reference electrode which has at least its tip immersed in the solution and a measuring electrode. The electrodes are connected to a variable potential or voltage source and generally to a recorder for recording the electrical response of the cell to the voltage change or some other parameter.
The electrodes may be mounted upon a cover which can be applied to the top of the cell.
Trace analysis for toxic substances in the environment, for example, require analytical methods and devices having high sensitivity precision and accuracy. For the determination of the level of environmentally toxic substances, therefore, such as heavy metals, herbicides, fungicides and insecticides, voltammetric methods have been developed because they fulfill these requirements.
In various fields, for example analysis of sea water, drinking water and fresh water sources, voltammetric methods of determining toxic compounds have been found to be preferable over other methods.
Naturally, because voltammetric methods are extremely sensitive, there is frequently the risk of contamination of the measuring vessel, of the cell, or of the measuring electrode with environmental contaminants which may not originally be present in the sample and which may be transferred to the cell during manipulation of the latter and/or during the normal operations in preparing the cell for an analytical run. These contaminants may arise from the atmosphere surrounding the cell, e.g. as the sample is introduced, or upon introduction of the electrodes or in some other similar manner.
Thus, relatively expensive apparatus was heretofore required to minimize the problem of environmental contamination and to keep the cell as free as possible from such contaminants during all phases of the operation.
Among other techniques for minimizing contamination was the use of vessels to receive the sample which were constituted of polytetrafluoroethylene or quartz.
Frequently there was also a desire to replace the measuring electrode for such cells either because a different type of measuring electrode was required or the original one became defective for some reason. This need was frequently incapable of being met in prior-art voltammetric systems because of the necessity to keep the cell free from contaminants and the danger that electrode replacement could introduce contaminants.
When the electrode was replaceable, however, the system was inordinately complex, expensive and otherwise disadvantageous.
For example, commercially available voltammetric cells (TACUSSEL) with replaceable measuring electrodes comprised a cover with a passage for the measuring electrode, the cell being also composed generally of quartz glass and having the auxiliary or reference electrode fused thereto, as well as a device for thermostatically controlling the temperature of the sample, for introducing a gas into the sample, etc. Such cells are difficult to clean and are so expensive that neither the cover nor the cell vessel can be considered to be "disposable" as is particularly desirable for high sensitivity measurements.
There are, however, also available cells (METROHM) which are easier to clean and which have, for example, a cover provided with openings in which each of the elements normally mounted in the cover can be fitted.
In this system, the cover fits upon a conical vessel and is held in place by a clamping bail or lever. Even these systems are highly expensive, ill-affording the luxury of one-time use, although they do provide advantages from the point of view of simpler cleaning and rapid closure.